Silicon integrated circuits designed for wireless communication and radar applications at millimeter (mm)-wave frequencies demand signal sources with high spectral purity. However, as the operation frequency increases, the implementation of low phase-noise oscillators becomes challenging. One possible solution is to utilize a frequency multiplier that up-converts its input driving source at a much lower frequency, where voltage-controlled oscillator (VCO) and phase-locked loop (PLL) with high spectral purity can be readily generated on chip.
Moreover, mm-wave signal sources generally require sufficient output power to serve as the local oscillator (LO) for frequency-translation circuits to drive the following power amplifiers. However, high power generation and efficient signal amplification are challenging at mm-wave due to limited transistor cut-off frequency fmax and break-down voltage in low-cost silicon processes. Therefore, conventional mm-wave frequency multipliers often suffer from high conversion loss, low direct current (DC) to radio frequency (RF) energy transfer efficiency, and limited output power.